Clock

ABSTRACT

A clock in which planetary gear wheels provided with inner teeth engage on stationary elements with outer teeth to obtain uniform rotation for successive gear stages. The eccentric drive of one stage necessary for engagement is directly effected by the eccentric shape of the rotating element of the preceding stage. The rotating elements belonging to each stage act as moving elements and also as indicating elements due to their markings.

United States Patent Hartwig 51 June 13, 1972 CLOCK 561 References Cited Inventor: Rudiger lhrtwig, Dresdoner Strasse 36. UNITED STATES PATENTS sindelfinsen- Germany 3,498,045 3/1970 Kemenczky ..58/7

[22] Filed: March 3, 1970 Primary mmir|erRtchard B. Wilkinson PP Assistant Examiner-Edith C. Simmons Anorney--Milton Robert Kestenbaum 1 Foreign A plication Priority Data ABSTRACT March 4, 1969 Germany ..P |9 10 818.0 A clock in Which planetary gear Provided with inner teeth engage on stationary elements with outer teeth to obtain uniform rotation for successive gear stages. The eccentric drive of one stage necessary for engagement is directly ef- [52] Cl 8' fected by the eccentric shape of the rotating element of the [5]] In 30 preceding stage. The rotating elements belonging to each [58] i "58/2 7 '25 g stage act as moving elements and also as indicating elements 75,804, due tome, markings 6 Claims, 16 Drawing Figures PATENTEMmamz 8.888.858

sum 20F 9 mvmrox. EUQIGER H'HEWIG,

PATENTEDJUMIHBIZ 3,668,858

' suwunr 9 IN VEN TOR.

PATENTEDJUH13 m2 3. 668,858

SHEET 6 n; 9

INVENTOR. RU DIGUL H'H ZTwIQ,

PATENTEBJUH 13 I972 3, 668. 858

saw 8 BF 9 INVEN TOR. 126 01601. PWZM! PATENTEnJuu 13 m2 SHEET 8 [IF 9 IN VEN TOR. Rd 0mm H'nmu i M w zltkaf CLOCK The invention relates to a mechanical arrangement for producing definitely reduced rotary movements of indicating or control elements operating successively in a plurality of 5 stages, particularly for clocks and control mechanisms.

The purpose of such arrangements is to convert a driving movement into a series of definitely reduced rotary movements, the progress or position of which can be visually read from outside by means of pointers or dials or can be for example electrically tested by means of contacts. In this connec tion, electrical or even mechanical contact arrangements usually serve the more simple purpose of actuating a control operation when a previously indicated position has been reached.

It is known practice to use, for the purposes of reduction, gear systems which consist of combinations of spur gears and worm wheels successively arranged (clockwork mechanisms). it is also known practice to provide, out of the usually large number of elements in such a gear system, those whose movement is of direct importance for indication with connecting elements (second, minute and hour wheels), to guide them out for the purpose of indication and to provide them with indicating elements (e.g. pointers). In addition, there are known systems in which the driving elements are provided with numerals on their periphery for the purposes of indication (mechanical counters), but they operate preferably intermittently to permit a clear reading and are designed for a series of identical reduction ratios for adjacent indicating elements (eg. I l0).

Apart from the gear wheels which are essential for indication, the use of spur gears only requires an additional number of intermediate wheels to obtain a standard rotation for indication. Furthermore, other elements are also required for guiding the indicating means as well as for the indicating means itself. The central indicating means in particular requires greater expenditure as regards the number of elements and their arrangement. in addition, further expenditure is necessary to permit adjustments within such a mechanism to be made from the outside (e.g. to adjust the minute hand) and this also affects the number of elements and the structure of the entire system. With control clocks it is known to provide a series of pre-selectable contacts over the periphery; however, these permit only a limited solution and therefore only a limited number of pre-selection times.

The problem underlying the invention is to provide an arrangement which minimizes the necessary number of such systems, to design the driving system so that possible divisional inaccuracies in components only produce minor errors, to substantially reduce the cost of manufacturing individual parts of the systems as well as assembly costs and possibly to permit even fully automatic assembly. Moreover, operations for example, when using a control clock can be accurately preselected to the minute or even to the second without causing a considerable increase in mechanical expenditure. Finally, a spring second pointer is obtained when used as clockwork and can also be adjusted in the second pointer when designed as a synchronous clock and can be synchronized, for example, with the television clock. All these requirements are fulfilled without departing from the normal appearance of the central pointer arrangement.

This problem is solved in accordance with the invention in that planetary gear wheels provided with inner teeth engage on stationary elements with outer teeth to obtain uniform rotation for successive gear stages in a modification of the basically main embodiments, the eccentric drive of one stage necessary for engagement being directly effected by the eccentric shape of the rotating element of the preceding stage. Because modified planetary gear stages are used in this manner, the same direction of rotation is directly obtained, and the number of moved elements in every stage may be reduced to a minimum (to one). Furthermore, high reduction ratios may be easily achieved in one stage (e.g. l 60 in a clock) since the difference in the number of teeth is essential for the degree of reduction (but not the quotient). The use of such stages in reduction makes it possible, if required, to provide teeth on a large segment of a circle, even outside the indicating field, and thus reduces the problems of tooth size as well as the effect of inaccuracies in the shape of teeth.

Another feature of the invention is that the rotating elements belonging to each stage act as driving elements, on the one hand, due to being the appropriate shape for that purpose and, on the other hand, as indicating or control elements due to their appropriate markings. Because of the central arrangement of all rotating elements which results from using such planetary gear stages, the rotating elements may be co-ordinated with the exception of driving and indicating operations and, in addition, control operations may be co-ordinated with likewise centrally arranged counter elements evenly distributed, for example, over the periphery of the frame. All additional elements are thereby rendered superfluous, i.e. those which are normally required to guide the indicating means, as an indicating element and, if necessary, as additional control wheels.

Another feature of the invention is that the elements provided with outer teeth for a plurality of successive gear stages are combined in the same component, and said component can also be the housing or frame of the clock. Thus several or even all the stationary elements in the form of individual parts which would have to be present at least once in every stage of reduction are omitted.

Other features of the invention are that a transmitting ele ment operates between the two rotating elements to transmit rotation from an eccentrically rotating element to a concentrically rotating element, which is to be driven at the same speed, within the same stage of reduction, said transmitting element being flexible in a radial direction, but tangentially rigid; that this element is designed as a detachable connection to vary the relative position of the two elements; that this element is a component of one of those elements which it connects. In this way the radial distance between the elements which is produced by the eccentric movement of the rotating element can be flexibly adjusted and balanced and at the same time, the rotary motion can be transmitted; that a relative adjustment between the two elements can be effected by disengaging the detachable connection; and that nevertheless no additional component is required.

Other features of the invention are that the rotating elements acting at the same time as driving and indicating elements are made of a transparent material and provided with appropriate externally visible markings; that the face showing the markings appears luminous as a result of the light guide effect produced by the appropriate shape of the surface when the light is projected from the side. Therefore, although the driving elements overlap one another, they can at the same time function as indicating elements; that the entire system, with the exception of the dial and pointers is transparent; and that in darkness only the dial and the hands are luminous when illuminated from below.

Another feature of the invention is that to use the rotating elements as control elements, the elements provided with outer teeth on the housing or another circle covered by the rotating elements are provided with contacts which can be externally tapped and insulated from one another, said contacts closing an electric circuit when touching the electrically conductive opposite contact on the rotating element, Thus, preselection for the control operation can be effected in a plurality of planes; reduction can be increased in any desired manner and, for example, in the case of the clock brings about preselection of the control operation accurate to the second by also providing the second-wheel with such means.

Another feature of the invention is that, when used as a clock, the rotating element used to indicate the seconds is tangentially driven via step-shaped teeth by a periodic lifting movement, whereupon a split second movement is executed particularly by 60 teeth on the driving wheel. A continuous or split second movement may be obtained thereby depending on the number of step-shaped teeth and the corresponding distance and frequency of the lifting movement.

Another feature of the invention is that a suitable adjusting element to be externally actuated acts upon the rotating element to adjust the second-hand and turns said rotating element in any desired manner independently of its drive. When using a drive with a power supply (synchronized clock) the second-hand can also be set during operation for a normal clock, for example, the television clock.

Other advantages and features of the invention are shown in the following description of three preferred embodiments.

FIG. 1 shows a concentric longitudinal section, true to scale, through the case of the clock, the drive and support having been omitted;

FIG. 2 shows an enlarged section of an assembly along the line 2-2 shown in FIG. 1;

FIG. 3 shows a view of the front section, true to scale, according to the arrow A in FIG. 1;

FIG. 4 shows a view of the minute section, true to scale, according to the arrow A;

FIG. 5 shows a view of the second section, true to scale, according to the arrow A;

FIG. 6 shows a view of the hour section, true to scale, according to the arrow A;

FIG. 7 shows a view of the rear of the case, true to scale, according to the arrow B;

FIG. 8 shows a concentric vertical section, true to scale, through the case of the clock in a second embodiment, the drive and support having been omitted;

FIG. 9 shows a view of the second, minute and hour sections according to the arrow C in FIG. 8, but in a staggered relationship to one another;

FIG. 10 shows an enlarged partial section of the driving portion of the clock;

FIG. II shows a concentric extended vertical section, true to scale, through the case of the clock in a third embodiment, the drive and stand having been omitted;

FIG. 12 shows an exploded perspective view of the clock according to FIG. 11',

FIG. 13 shows a section similar to FIG. 11, but with the clock having been assembled;

FIG. I4 shows a general perspective view of the clock together with the stand;

FIG. 15 shows a front view ofthe clock;

FIG. 16 shows a perspective view of the clock similar to FIG. 14 before the case is mounted on the stand.

All the parts described below are produced by injection moulding and are made of a plastic glass. They can be already assembled, but in case assembly may be wrongly effected, they may be delivered individually to the user so that he may assemble them himself.

A square front section II has a circular bore 13 with a center about a first geometrical longitudinal axis 12. A dial 14 divided into the usual [2 hours is provided symmetrical to the longitudinal axis 12.

A minute section 16 comprises a disc 17 which is symmetrical to the geometrical longitudinal axis 12 and can be rotated about said axis, the outer periphery 60 of said disc having upwardly pointing rectangular teeth 18 of equal size which are supported on a diameter 19 measured from the longitudinal axis 12. Moulded to the left-hand side shown in FIG. 1 is a knob 21 which penetrates the bore 13 and with which the minute section 16 can be adjusted at random. To the righthand side of the disc 17 is moulded a disc 22 coaxial with the longitudinal axis 12, said disc 22 being in the vicinity of the hub of the disc 17 and its height being greater than the width of a second section 23. The disc 22 is connected to a disc 24, the latter having its center in a second longitudinal axis 26 which is eccentric to the first longitudinal axis 12. It also has a smaller diameter than the disc 22. As can be seen in FIG. 4, it is arranged so that the outer circumferences of the two discs 22, 24 are never aligned, but a step 27 always remains at the narrowest point. The disc 24 is approximately the same height as the disc 22. On the disc 17 there is a minute hand 28 which can be integral with said disc, adhesively attached thereto, etc.

The second section 23 comprises a disc 29, the external diameter of which is slightly greater than that of the disc 17. Its outer circumference is provided with 60 identical saw-teeth 31 extending in the same direction, the only exception being the shape of a saw-tooth 32. With the exception of the latter all the saw-teeth are supported on the same diameter 33 which is greater than the diameter 34 of the minute section l6. The flattened-out flank 36 of the tooth 32 extends so far into the disc 29 that a carrier 38 located on the base 37 of the flank 36 and shown by broken lines in FIG. 7 can pass together with its projecting end 39 between two teeth 18 of the minute section 16 and move the latter and the second section 23 by the length of one tooth. A second hand 4] of the disc 29 points in almost exactly the opposite direction to the saw-tooth 32. The disc 29 which is coaxial with the longitudinal axis 12 has a circular bore 42 and is rotatably guided therewith over the circumference of the disc 22.

An hour section 43 comprises a disc 44 having a smooth outer circumference. As can be seen in FIG. 1, this disc 44 has the smallest diameter of all the discs 17, 29. An hour hand 46 is provided thereon and an inner toothed wheel 47 having twelve identical inner teeth 48 is moulded in the form of a hub to the disc 44. The inner toothed wheel 47 is coaxial with the longitudinal axis 26, and likewise the circular bore 49 by means of which the hour section 43 is supported on the eccentric disc 24 with a minimum of play.

A rear wall 51 of the clock case has a slightly bigger base 52. It has the same outer shape as the front ll of the case and a circular recess 53 coaxial with the longitudinal axis 12, into which fit all the discs I7, 29, 44. Also coaxial with the longitudinal axis 12 is a pin 54 which penetrates, but does not touch the bore 42, 49 and extends into a coaxial pocket hole 56 of the minute section with a minimum of play. A toothed wheel 57 having outer teeth 58 is introduced into the base 52. As can be seen in FIG. 2, the outer teeth 58 are in the form of small cylinders and the inner teeth 48 have corresponding flanks. The shape of the teeth is not important; other more common shapes could be selected for the teeth. The wheel 57 has eleven outer teeth 58 which are identical in shape and evenly distributed around the circumference. Around the toothed wheel 57 there is provided a recess 59 in which the inner toothed wheel 47 is accommodated. A driver 38 shown by broken lines is inserted e.g. in channels 61, which driver can be moved back and forth by a drive according to the double arrow 63 and extends approximately tangentially to the disc 29. At the top there is provided a radial slot 64 through which a strip 66 is guided, and can slip partially downwards and move up and down over the circumference of the disc 29. The minute section 16 has an unshown overlocking device which co-operates with the teeth 18.

The clock operates as follows:

Every second the driver 38 moves to the left and carries the disc 29 through 6 along the steep side of the saw-teeth 31, 32. On the return movement the projection 39 slides upwards along the flat side of the teeth 31, 32 and the strip 66 prevents a reverse rotation. When the projection 39 moves into the base 37 of the saw-tooth 32 it only carries the disc 17 of the minute section 16 in this case because it can pass between the teeth 18. If, therefore, the disc 29 passes through 360, the disc 17 is moved through 6 with spasmodic accuracy at the point between the final second of the preceding minute and the first second of the following minute.

The eccentric disc 24 attached to the minute section 16 together with the bore 49 of the hour section 43 causes the inner toothed wheel 47 to rotate about the toothed wheel 57 once every minute. Assuming that rotation takes place in the direction of the arrow 68, after rotating for 1 hour a given inner tooth 67 is no longer located at the point shown in FIG. 2, but at that point which is occupied by a special inner tooth 69 in FIG. 2. Thus the hour section 43 has moved in a clockwise direction through 30. In this connection the longitudinal axis 26 is moved on the circle 65 shown by a broken line in the direction of the arrow.

The described invention is suitable for conventional 12 hour, 60-minute and (SO-second clocks, but it can be easily modified if a 24 hour, hundred-minute and a hundred second clock is required. For example, 24 outer teeth 58 and 25 inner teeth 48 would then have to be provided.

If the clock is not to be read directly, but used for example as a control clock, the pointers 28, 48, 46 can be replaced by corresponding contacts. In the case of the clock it is possible to accept unusually large tolerances in manufacture. The sequence of the discs 17, 29, 44 can be altered, for example, by positioning the disc 24 on the left-hand side of the disc 17. Furthermore, the rear wall 51 can be designed as a clock face so that the front section 11 constitutes the base in this case. The front section 11 and the rear wall 5] of the clock are rigidly and, if necessary, releasably connected by unshown means.

The advantage of the clock described is that it can be turned back or adjusted by the knob 21, since rotation of the minute section 16 causes a corresponding rotation of the hour section 43. In cases where it is unnecessary for the clock to be turned back or adjusted or where another form of adjustment is possible, the second embodiment according to FIGS. 8 to 10 is suitable. FIG. 8 shows the front section 11, the rear wall 51, and the recess 53 in which fit the second section 23, the minute section [6 and the hour section 43. There is only a single longitudinal axis 12 in relation to which the pin 54 is coaxially arranged in the recess 53 and the second section 23, the minute section 16 and the hour section 43 are rotatably mounted in corresponding concentric bores. The circumference of the second section 23 is also provided with teeth 31, in addition to which there is the tooth 32. However, in contrast to the first embodiment the flank 36 is considerably more inclined and extends so far into the second section 23 that, as can be seen particularly clearly in FIG. 10, a pawl or catch 71 can move as far as the teeth 72 of the hour section 43. This can only be achieved if the point 73 is located in the base 37 of the tooth 32 and if at the same time the minute section 16 has a tooth 74 with a flank 76 which is not so deeply recessed as the flank 36. As can be seen from the drawings, the minute section 16 is also provided with saw-teeth. The saw-teeth of the second section 23, the minute section 16 and the hour section 43 all extend in the same direction. As can be seen in FIG. 9, I l teeth 18 are located between two teeth 74 of the minute section 16. Every l2th tooth therefore has a special shape which means in the practical embodiment that every l2 minutes the point 73 can engage in both the tooth 32 and in one of the teeth 74 so that the hour section 43 is moved by the length of one tooth every 12 minutes. The circumference of the second section 23 is provided with 60 teeth, as is the minute section 16 which includes specially shaped teeth. The hour section 43 is also provided with 60 teeth, all being identical in shape. In this connection the discs are made of a transparent plastics material so that the associated pointers are externally visible.

As can be seen in FIG. 10, the pawl 71 can execute a pivoting movement according to the curved double arrow. Furthermore, it can perform a lifting movement according to the straight double arrow. The necessary means for preventing rearward movement are not shown. These can have a variable shape and the drive of the clock can also be different in design. The upper end of the point 73 has a straight cutting edge, but the second, minute and hour sections, 23, I6 and 43, could be given the same external diameter and a correspondingly stepped cutting edge could be used in place of a straight cutting edge. The hour section 43 in the embodiment moves through 6 every 12 minutes. In this case therefore the hour section 43 can be accurate to the second when springing into the hour position.

The units of time in the embodiment are seconds, minutes and hours, but other units of time could also be used such as for example. a third of a second or 2 seconds etc. The number of teeth would then be altered accordingly.

The third embodiment according to the FIGS. ll to 16 is suitable when it is intended to drive the part showing the lowest unit of time, i.e. the second section 23 in the embodiment. In the drawing the shapes of the front section 11 and the rear wall 51 have been exchanged and the pocket hole 56 is a circular bore in this case. On the front section II of the clock are shown the stationary pins 54 and the toothed wheel 57 with ll outer teeth 58, the l2 inner teeth 48 of the inner toothed wheel 47, the bore 49 and the hour-hand 46. A toothed wheel 77 having 59 outer teeth 78 is concentric with the longitudinal axis l2 on the front section II of the clock. The minute section 16 has a peripheral edge 79 which is concentric with the longitudinal axis 12, and a resilient transmitting element 81. Between the minute section 16 and the second section 23 there is an intermediate ring 82 bearing an externally smooth inner toothed wheel 83 which projects to the left as shown in FIG. 11 and has 60 inner teeth 84. The inner teeth 84, cooperate with the outer teeth 78 in the same manner as the inner teeth 48 cooperate with the outer teeth 58. The inner toothed wheel 83 engages with a minimum of play in an outer ring 86 which is eccentric with the geometric longitudinal axis I2. The ball 42 is concentric with the longitudinal axis 12. These drawings are shown true to scale, but the eccentricities have been deliberately magnified. They transmit only l/l20 (in the case of l:60) or H24 (in the case of 1:12) of the diameter of the ring. In the case of a dial having a diameter of approximately l2 c.m., an eccentricity of only 1 mm. is produced for both eccentrics and is proportionally less for smaller embodiments.

The operation of the mechanism is described with the aid of FIGS. II and I2. A lifting movement every second serves as a drive according to the arrow 87 and acts tangentially on the second section 23. In this way the second section 23 rotates jerkily through one sixtieth of a revolution per second. At the same time the eccentric arrangement of the outer rings 86 which slides over and engages the intermediate ring causes the latter to rotate about the toothed wheel 77 through only one sixtieth of a revolution whenever the second section 23 completes a full revolution. The resilient transmitting element 8] on the minute section 16 which is easily guided to the left and right engages in the inner teeth 84 of the intermediate ring 82 and transmits the rotary movement of the intermediate ring 82 to the minute section 16. Therefore the minute section 16 rotates concentrically at the speed of the minute hand. The eccentric disc 24 on the minute section 16 which slides into the bore 49 causes the inner teeth 48 of the hour section 43 to rotate on the outer teeth 58 of the toothed wheel 57. In this way, whenever the minute section 16 completes a full revolution, the hour section 43 rotates through one twelth of a revolution, therefore at the speed of the hour hand. The hour section 43 is the only one of the three indicating elements in which a slight eccentric movement is added to the rotary movement, but this is in no way detrimental to the hour section because of its very slow speed. The minute section 16 is adjusted from the outside by the knob 21, the resilient transmitting element 81 engaging on any of the inner teeth 84 of the intermediate ring 82. Since the intermediate ring 82 has a total of 60 teeth, automatic adjustment can only be effected in complete minutes. Therefore the minute hand 28 always points exactly to a minute mark when the second hand 41 passes through 12. This clear coordination between the two pointers is not possible with clocks having the means for continuous adjustment.

All the reduction teeth can be arranged outside the field of vision, as is the case with the teeth 78, 84, in the ratio of 59/60. For the minute/hour reduction 55/60 teeth would be preferable to l l/ 12 teeth.

FIG. 14 shows a clock with such a driving means. The drive can be effected e.g. by a synchronous motor, the speed of which is reduced from e.g. 50 revolutions per second to one revolution per second by a further stage in the planetary gear being flat in design, said two parts being inserted in a base stand 88. FIGS. 15 and I6 show basically how the transmission from the base stand 88 to the mechanism of the clock can be effected and also show how simply the wheels are connected to the driving system. The position of the second-hand 41 can be altered independently of the drive by a simple handoperated advance mechanism e.g. in the form of an externally operated pressure rod system which is provided with a resetting spring and, when actuated, has a rotating effect on the second section 23. In this case also step-wise adjustment is only possible in complete seconds since 60 teeth 31 are provided on the circumference of the second section 23. This means that whenever this clock is adjusted to a normal clock having a spring second, the phase between the second hands of both clocks remains the same in any other position, once it is correctly adjusted.

The illustrated embodiment also acts as a control clock if the teeth on the front section 11 of the clock are in the form of contacts which are insulated against one another and can be connected to an outer circuit eg by small plugs or an adjustable sliding contact. Every point on the inner teeth of the hour section 43 and the intermediate ring 82 must also be conductive and in addition conductively connected. When the previously connected contacts on the front section ll reach the conductive points on the hour section 43 and the intermediate ring 82, the circuit is closed and the control operation is performed with accuracy to the minute. By also providing the second section 23 with corresponding contacts an embodiment showing accuracy to the second may be also obtained by an extended series connection. The contacts for all pre-selection planes and their leads can be fitted in the front section ll of the clock.

What I claim is:

l. A time-keeping instrument comprising a case,

an outer toothed wheel rigidly attached to said case and arranged coaxially about a first longitudinal axis,

a first time indicating element indicating the maximum unit of time for the instrument and having a circular bore at its hub having a second longitudinal axis which moves intermittently eccentrically relative to said first longitudinal axis,

an inner toothed wheel rigidly connected to said first time indicating element and having more inner teeth than the outer toothed wheel has outer teeth and a larger diameter of contact than the outer toothed wheel and being rolled on the outer toothed wheel,

a second time indicating element indicating the next smaller unit of time, supported by said case rotatably about said first longitudinal axis and having a first circular disc engaging and rotatably supporting said first time indicating element in said circular bore and moving intermittently about the eccentricity of the two longitudinal axes to drive said first time indicating element, and having teeth at its circumference equal in number to its time unit and having a second circular disc arranged coaxially with said first longitudinal axis,

a knob rigidly connected to said second time indicating element for turning same, rotatable coaxially with said first longitudinal axis,

clock driving means,

a third element supported by said second disc and rotatable about said first longitudinal axis, having teeth at its circumference equal in number to the periodic driving frequency of said clock driving means, one of said teeth being followed by a gap deeper than the depth of the other teeth,

said clock driving means being laterally arranged and engaging the teeth of said third element and also engaging a tooth on said second time indicating element when engaging said gap,

2. An arrangement as claimed in claim I in which the circumference of the third element is provided with teeth corresponding to the number of seconds; an adjacent circumference of the second element is provided with teeth corres onding to the number of minutes; the teeth of the second an minute sections are supported on different diameters; and

a flank of only one tooth of the second section is guided into a portion corresponding approximately to the diameter on which are supported the teeth of the minute section.

3. An arrangement as claimed in claim 2, characterized in that the two discs lie on the same side of the minute section in that the second disc has a considerably larger diameter than the first disc and in that the first disc is located on the second disc.

4. An arrangement as claimed in claim 2, characterized in that the circumference of the second section and the minute section is the outer circumference in each case, in that the minute section and the second section are flat discs which are made of a transparent plastics material for visual reading, and in that the external diameter of the minute section is at the most the same as, the internal diameter of the teeth on the second section.

5. An arrangement as claimed in claim 2 in which the teeth of the second section are in the form of saw-teeth, and in that the teeth ofthe minute section have a symmetrical shape.

6. An arrangement as claimed in claim 2 in which a radial slot is provided in the case above the second section, and a strip the lower edge of which is supported on the circumference of the second section, is vertically movable through the slot. 

1. A time-keeping instrument comprising a case, an outer toothed wheel rigidly attached to said case and arranged coaxially about a first longitudinal axis, a first time indicating element indicating the maximum unit of time for the instrument and having a circular bore at its hub having a second longitudinal axis which moves intermittently eccentrically relative to said first longitudinal axis, an inner toothed wheel rigidly connected to said first time indicating element and having more inner teeth than the outer toothed wheel has outer teeth and a larger diameter of contact than the outer toothed wheel and being rolled on the outer toothed wheel, a second time indicating element indicating the next smaller unit of time, supported by said case rotatably about said first longitudinal axis and having a first circular disc engaging and rotatably supporting said first time indicating element in said circular bore and moving intermittently about the eccentricity of the two longitudinal axes to drive said first time indicating element, and having teeth at its circumference equal in number to its time unit and having a second circular disc arranged coaxially with said first longitudinal axis, a knob rigidly connected to said second time indicating element for turning same, rotatable coaxially with said first longitudinal axis, clock driving means, a third element supported by said second disc and rotatable about said first longitudinal axis, having teeth at its circumference equal in number to the periodic driving frequency of said clock driving means, one of said teeth being followed by a gap deeper than the depth of the other teeth, said clock driving means being laterally arranged and engaging the teeth of said third element and also engaging a tooth on said second time indicating element when engaging said gap.
 2. An arrangement as claimed in claim 1 in which the circumference of the third element is provided with teeth corresponding to the number of seconds; an adjacent circumference of the second element is provided with teeth corresponding to the number of minutes; the teeth of the second and minute sections are supported on different diameters; and a flank of only one tooth of the second section is guided into a portion corresponding approximately to the diameter on which are supported the teeth of the minute section.
 3. An arrangement as claimed in claim 2, characterized in that the two discs lie on the same side of the minute section in that the second disc has a considerably larger diameter than the first disc and in that the first disc is located on the second disc.
 4. An arrangement as claimed in claim 2, characterized in that the circumference of the second section and the minute section is the outer circumference in each case, in that the minute section and the second section are flat discs which are made of a transparent plastics material for visual reading, and in that the external diameter of the minute section is at the most the same as, the internal diameter of the teeth on the second section.
 5. An arrangement as claimed in claim 2 in which the teeth of the second section are in the form of saw-teeth, and in that the teeth of the minute section have a symmetrical shape.
 6. An arrangement as claimed in claim 2 in which a radial slot is provided in the case above the second section, and a strip the lower edge of which is supported on the circumference of the second section, is vertically movable through the slot. 